Eliminating hydrogen sulfide odor
during the process of forming wet
strength paper containing cereal
xanthates



United States Patent ELIMINATING HYDROGEN SULFIDE ODOR DURING THEPROCESS OF FORMING WET STRENGTH PAPER CONTAINING CEREAL XANTHATES DonaldH. Wheeler, Minneapolis, Minn., assignor to General Mills, Inc., acorporation of Delaware No Drawing. Filed Apr. 16, 1964, Ser. No.360,415 4 Claims. (Cl. 162-175) The present invention relates to aprocess of paper manufacture which involves the use of cereal xanthatesas wet strength additives.

Cereal xanthates have recently been suggested as wet strength additivesfor paper products. To accomplish this, the cereal xanthate iscross-linked by the use of an oxidizing agent to form the xanthide.However, in this operation frequently H 8 is given off which isobjectionable in most paper processing plants.

It has now :been discovered that by means of the present invention it ispossible to cross lin'k the cereal xanthate to the xanthide without theproduction of any objectionable quantities of H 8. In addition,surprisingly enough it is found that the wet strength of the paper isimproved by the present process as compared to certain prior suggestedprocesses.

The reactions involved in the formation of the xanthate and thecross-linking of the xanthate to the xanthide are illustrated in thefollowing equations:

ROH NaOH OS, ROCSSNa xanthate I] i 2ROOSSNa Oxidizing Agent ROCSSU ORxanthide In the above equations R is the residue of the starch moleculefound in typical cereal starting material. The starting materials may becereal starches, but because of the cost element, the starting materialis preferably a low grade flour or a millfeed commonly referred to inthe trade as .bran. Because of its preference from a cost standpoint,the detailed description will be with particular reference to Ibran. Inthe xanthation reaction the bran may be reacted with the sodiumhydroxide or other alkali metal hydroxide and the carbon disulfideeither in the form of a dilute solution or dispersion or in the form ofa concentrate in which event the xanthate is obtained in the form of astiff gel or as a particulate moist powder at low levels of watercontent. In either event a solution of the xanthate is used in the papermaking operation. The xanthate solution is added to the pulp anddispersed therein. In certain prior art processes the pH of the pulpdispersion has been adjusted to 7 or even down to 4 or 5 by the additionof acid and then an oxidizing agent is added for the purpose ofcross-linking the xanthate to the xanthide. A variety of oxidizingagents may be used for this purpose but chlorine or the hypochlorite arepreferred for reasons of ready availability and economy. When thisprocess is carried out it is found that rather large amounts of H 8 a-reevolved in the neutralization step of the paper making operation andthese are objectionable.

It has now been discovered, however, that it is possible to neutralizeonly part of the alkali used in preparing the xanthate and to add thenthe cross-linking oxidizing agent and thus eliminate the problem of H 8.in the preferred operation the cross-linking is effected by bubblingchlorine gas through the pulp dispersion which served the purpose, notonly of cross-linking by oxidation but also served to acidify the pulpto a pH of 6 or lower.

Attempts were made in the past to use the chlorine both as an acidifyingagent and as the cross-linking oxidant. Under these circumstances it wasfound that H S was not evolved but actually the quality of the paper wasimpaired as compared with the use of a regular mineral acid as apreliminary neutralizing agent prior to the use of the cross-linkingoxidant. It has been found that when from 10% to about 65% of the alkaliused in forming the xanthate is neutralized by a strong mineral acidsuch as sulfuric or hydrochloric prior to the addition of across-linking oxidant that there is virtually no H S formed when thepulp is ultimately acidified and converted into paper. When less thanabout 10% of the alkali is neutralized prior to the addition of theoxidant the improvement in wet strength falls off as compared withpreliminary neutralization within the range of 10% to 65%. Likewise,when one attemps to neutralize more than about 65% of the alkali priorto the addition of the oxidant, it is found that increasing quantitiesof H 8 are evolved.

The following examples will serve to illustrate the invention.

Example I 5 grams of ground bran, at 5% moisture (0.0293 mole ofanhydroglucose units), was stirred with 50 ml. of H 0. To this was added2.9 ml. of 30% NaOH solution by weight (1 mole NaO H per anhydroglucoseunits of bran) and thoroughly mixed by stirring. To this mixture wasadded 0.74 g. of CS (0.3 mole per anhydroglucose unit of bran). Thereaction was allowed to proceed for 15 minutes at room temperature. Thereaction mixture remained as a stirrable, pourable liquid at all stages.

The above dispersion was immediately added to 24 g. of unbleachedsulphite paper pulp which was dispersed in 3.2 liters of water. Themixture of cellulose paper pulp and xanthate was partially neutralizedby addition of 4 ml. of 10% H 50 (approximately 32% of the H 80 neededto neutralize the NaOH used in making the xanthate). Chlorine gas wasthen bub-bled into the mixture with stirring until the pH was lowered to6 (required 0.82 g. of C1 No odor of H 5 was observed during thisacidtllation, as well as during the oxidation by chlorine. The mixturewas stirred for 15 minutes, after which it was made into hand sheets (3sheets test paper) size 12 inches by 12 inches and weighing about 8grams each. The sheets were pressed on a screen between felts and thendried in a steam heated dryer. Similar sheets were made without theadditive (control). The control and sample sheets were equilibrated in aroom at F. at 50% relative humidity. The sheets were then weighed inorder to calculate tensile strength at identical sheet weights. The 4.75g. of bran (dry basis) represents a 20% addition of bran as xanthate tothe cellulose pulp. The control sheets were tested [for mullin burststrength in the dry state for a reference value. The control sheets whenimmersed in H O for /2 hour gave wet burst of 1 to 2% of the dry burst.The sheets containing bran made according to this example gave wet burstof 39% of the dry control.

A series of examples were run in which variations were made in therelative amount of sodium hydroxide and canbon disulfide used in thexanthation and in which varying amounts 01f the NaO'I-I wereneutralized. The results are given in the following table:

1 With 20% bran xanthate added to paper; wet burst as percent of dryburst of control without additive.

It will be evident from the above table that various ratios of NaOH andCS to anhydroglucose units may be employed, and similarly that thedegree to which the NaOH is neutralized may be varied. The table alsodemonstrates that when the NaOH is not neutralized, at least in partprior to the addition of the chlorine the wet burst strength of thepaper is impaired. The amount of xa-nthate used in the paper can bevaried over considerable limits. Generally however it is preferred toemploy at least 5% of the xanthate based on the weight of the paper andit may go as high as 40% or more of the weight of the paper. Theparticular quantity to be employed depends upon the particular degree ofwet strength and other properties desired in the paper and the cost ofthe .paper relative to the properties.

Numerous other modifications of the invention may he made withoutdeparting from the spirit thereof as defined in the following claims.

The embodiments of the invention in which an exelusive property orprivilege is claimed are defined as lfOllOWSZ 1. In a process of makingpaper from a pulp slurry which includes the incorporation in the pulpslurry of an alkali metal xanthate selected from the group consisting ofxanthates of cereal starches, flour and bran and cross-linking saidxanthate by means of an oxidizing agent selected lflOlTl the groupconsisting of chlorine and hypochlorite prior to the formation of paperfrom said slurry which process normally results in the liberation ofobjectionable quantities of H 8, the step of substantially eliminatingthe liberation of objectionable quantities of H 8 which comprisesneutralizing the alkali used in forming the xanthate to an extent offrom about 10 to 65% of said alkali by means of a strong mineral acid.

2. Process according to claim 1 in which approximately 50% of the alkaliused in forming the xanthate is neutralized prior to the addition of theoxidizing agent.

3. Process according to claim 1 in which the oxidizing agent ischlorine.

4. Process according to claim 1 in which the xanthate is employed in aproportion from about 5 to based on the weight of the paper.

OTHER REFERENCES Russell et al.: Tappi, vol. 45, No. 7, July 1962, pp.557- 566.

DONALL H. SYLV ESTER, Primary Examiner.

S. LEON BASHORE, Examiner.

1. IN A PROCESS OF MAKING PAPER FROM A PULP SLURRY WHICH INCLUDES THEINCORPORATION IN THE PULP SLURRY OF AN ALKALI METAL XANTHATE SELECTEDFROM THE GROUP CONSISTING OF XANTHATES OF CEREAL STARCHES, FLOUR ANDBRAN AND CROSS-LINKINGN SAID XANTHATE BY MEANS OF AN OXIDIZING AGENTSELECTED FROM THE GROUP CONSISTING OF CHLORINE AND HYPOCHLORITE PRIOR TOTHE FORMATION OF PAPER FROM SAID SLURRY WHICH PROCESS NORMALLY RESULTSIN THE LIBERATION OF OBJECTIONABLE QUANTITIES OF H2S, THE STEP OFSUBSTANTIALLY ELIMINATEING THE LIBERATION OF OBJECTIONABLE QUANTITIES OFH2S WHICH COMPRISES NEUTRALIZING THE ALKALI USED IN FORMING THE XANTHATETO AN EXTENT OF FROM ABOUT 10 TO 65% OF SAID ALKALI BY MEANS OF ASTRONGN MINERAL ACID.